Of all the issues raised by the NIH single-IRB policy, the relationship between the single IRB and the participating sites is possibly the most complex. There are 3 critical aspects that academic institutions, researchers, and policy makers will have to resolve before implementation of the new policy: (1) the relationship between the single IRB and the local institutions, including the local IRBs; (2) the collection and incorporation of local knowledge in the single-IRB review; and (3) the relationship between the single IRB and local researchers. These issues involve fundamental legal, ethical, institutional, and policy tensions that will profoundly shape the costs and effectiveness of future multisite research involving human research participants.